 A visual comparison of the size of Earth and CoRoT-7b. (Source: geology.com)
With surface temperatures hot enough to vaporize silica, scientists probably won't find much life here.
February of last year saw a small but
possibly noteworthy extra-solar planet discovered by the French CoRoT
mission. The CoRoT device, launched December 27, 2006, lives a
dual-purpose mission. It both searches for extra-solar planets and
measures stars for active seismology. CoRoT stands for Convection
Rotation and planetary Transits, and these transits are what
generally give away extra-solar planets far away from home.
In
October of last year, the CoRoT team confirmed that the planet
discovered in February, named CoRoT-7b, was the first extra-solar
planetary body that came close to being Earth-like in stature and
composition. CoRoT-7b orbits its home star CoRoT-7, usually
classified as a G9V yellow dwarf (our Sun is a G2V classification for
comparison and slightly larger), along with relative CoRoT-7c,
somewhere in the area of 490 light years from Earth. CoRoT-7 can be
found in or near the constellation Monoceros.
For the
astronomically interested, Monoceros is not a bright constellation;
it's brightest star coming in at 3.93 magnitude with several between
four to six. However, it is easily found as it resides just west and
south of the easily identified Orion constellation. Drawing a line
between Betelgeuse of Orion and Sirius of Canis Major will get you
pretty near to Gamma Monocerotis, the second brightest star in the
constellation, and one end of its line form.
Other than
CoRoT-7, Monoceros’s area also contains other astronomical bodies
of note, including a trinary star system, two binary star systems,
one of which is the well-known Plaskett’s Star, and V838
Monocerotis, a star which flared in January of 2002 and produced
stunning images via the Hubble Space Telescope.
Getting back
to CoRoT-7b, researchers have inferred a great deal about the planet
using various astronomical means. It is so far the closest to Earth
in size found outside our solar system, coming in at just 1.7 earth
radiuses. It is also similar in density to Earth, though it has a
mass about five times greater. But this is about where the
similarities end.
CoRoT-7b is a hot planet. Very very hot. It
is so close to its star that its lit face burns at an estimated
4,000F while its dark side could drop as low as minus 350F. The
planet’s orbital duration is also the shortest of any known planet,
whirling around CoRoT-7 in a mere 20.5 hours. The distance between 7b
and 7 is a mere 2.5 million kilometers. For comparison, Mercury is
roughly one third the size of Earth, orbits the Sun at just over 46
million kilometers distance at perihelion in a period just under of
88 days and has surface temperatures of a balmy 800F to minus
300F.
CoRoT-7b is thought to be mostly composed of iron, but
not as densely as Earth. Any volatile atmosphere would likely have
been stripped away by the intense heat of CoRoT-7, though some
scientists have proposed it may have metallic atmosphere which rains
out minerals.
To make 7b even more notable as an extra-solar,
Earth-like planet, scientists at the University of Washington have
recently disclosed that unless the planet has a perfectly circular
orbit, it is likely the most geologically
active planetary body yet known. A variance between its orbital
aphelion and perihelion (furthest and closest from its orbital center
point) as little as 250 kilometers would cause great stress and
friction to the planet's interior, driving what could be a
planet-wide volcanic system. Jupiter’s moon Io, the most active
body in our solar system, would look like an afternoon breeze
compared to 7b’s hurricane winds.
Though the planet has much
more mass than Io, and even Earth, there are almost certainly no
liquid oceans to absorb tidal forces in the way Earth’s do. The
gravitationally driven geological processes would closely mimic Io’s,
as Jupiter and its other large moons tug on it during its orbit, but
would be much more extreme due to the magnitudes greater of the
forces being applied.
Though the find and subsequent analysis
of CoRoT-7b has been a great achievement for astronomers, planetary
scientists and planet finders, it is still not the life-harboring
extra-solar planet most hope to discover. Given the number and type
of extra-solar planets discovered thus far, it may require even more
precise measuring systems floating above our atmosphere to catch the
tiny tugs and magnitude fluctuations an Earth-sized planet would
affect on a Sun-sized star.
"Because it is easier to
detect planets that orbit close to their host stars, a significant
fraction of the first wave of rocky planets being found outside our
solar system may be more Io-like than Earth-like," explains UW
postdoctoral researcher of astronomy and astrobiology Rory
Barnes.
However, if the last twenty or even ten years of space
programs have taught us anything, it’s that we have nowhere to go
but up.
"Mac OS X is like living in a farmhouse in the country with no locks, and Windows is living in a house with bars on the windows in the bad part of town." -- Charlie Miller
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